This invention relates to ammunition casings, and more particularly to an improved composite ammunition casing made up of a plurality of component parts, including a tubular metallic forward casing member, a tubular rear casing member, and a head assembly for reinforcing the base of the casing and mounting a primer component.
The principal purpose of composite ammunition casings is to permit the use of dissimilar materials for the components, usually comprising plastic for the casing body and metal for the head assembly, thereby conserving the relatively scarce and expensive metal. Examples of such composite casings are described and claimed, for example, by U.S. Pat. No. 3,745,924 issued July 17, 1973 to John J. Scanlon, and by U.S. Pat. application SER. No. 320,328, filed on Jan. 2, 1973 by H. Jackson Hale, and now U.S. Pat. No. 3,874,294, both of which are assigned to the owner of this application. The mouth portion of the casing may be integrally formed in the casing body, or may be a separate insert, usually of metal. A composite casing of the latter type is described and claimed by U.S. Pat. No. 3,842,739 issued Oct. 22, 1974 to John J. Scanlon et al, and also assigned to the owner of this application.
The general object of the present invention is to reduce, or to eliminate altogether, the need for using relatively expensive plastic materials having high temperature resistance characteristics in composite ammunition casings, particularly in casings of a type intended to be used in repeating guns and firearms whose receiving chambers tend to develop a temperature gradient along their lengths. Further objects and advantages of the invention will appear as the following description proceeds.
Research on repeating firearms and guns, particularly of the military type, has demonstrated that it is advantageous to employ a metal mouth insert with a plastic casing body, such as in the casing disclosed by the aforementioned U.S. Pat. No. 3,842,739. This affords better retention of the projectile, and also places the center of gravity of the casing farther forward than in one made entirely of plastic, so that the casing exhibits dynamic behaviour like that of an all-metal casing although it is lighter in weight. It therefore cooperates more satisfactorily with a standard ejection mechanism.
However, inexpensive plastics having relatively low temperature-resistance characteristics, such as polysulfones and polyethylenes, which are satisfactory for ammunition casings for many firearms, especially those of the smaller calibers, are precluded from use in ammunition casings of previously-known designs for many repeating firearms, and for guns of larger calibers. The receiving chambers of such firearms become heated upon firing, with a temperature gradient ranging from a maximum at the forward throat of the chamber to a minimum at the rear breech portion. Illustratively, this gradient may range from 550.degree. to 330.degree. F. in a typical 30mm gun. To avoid casing failure, it has previously been necessary to use a relatively expensive plastic having a high temperature-resistance characteristic, such as a tetrafluoroethylene polymer, for the bodies of composite casings to be used in such weapons. The plastic may comprise about half the casing weight, especially in larger calibers such as 20 and 30mm, so that the expense becomes excessive.
Briefly stated, according to a preferred embodiment thereof, I carry out my invention by forming a composite ammunition casing from a metallic forward tubular casing, and a rear tubular casing made of a material having a lower temperature-resistance characteristic than the metal of the forward casing. This material may be one of the less expensive plastics such as polyester, polysulfone, or polyethylene polymers.
The forward metallic casing member is extended rearwardly a substantial distance from its mouth, and meets the rear casing member at a distance which is to be selected on the basis of a determination of the temperature gradient to be encountered in the type of firearm or gun in which the casing is to be used, and the limit of temperature resistance of the particular material chosen for the rear casing member. The junction is located at a distance from the mouth of the casing at which the temperature of the chamber drops below the upper limit which is tolerable by the rear casing without excessive loss of strength.
The forward and rear casing members are connected at this junction by an interlocking gas-sealing joint, which preferably is formed by interruptions in the wall surface of the forward casing member, into which some of the material of the rear casing member projects. The term "interruptions" is employed to generally describe recesses, holes, threads or the like in the otherwise tubular forward casing wall. If the rear casing member is formed of an initially-flowable plastic material, the joint is preferably completed by insert molding, that is, by molding the rear casing member with the forward casing member inserted in the mold, so that the projections of the rear casing into the discontinuities of the forward casing are formed in situ. The interlocking joint may, however, be formed by threads, by cement if of sufficient strength for the purpose, or by other known securing means.
The rear casing member terminates in a base portion, to which a head assembly of known type may be attached.